JP2018093202A - R-t-b based permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an R-T-B based permanent magnet showing high residual magnetic flux density Br and coercive force HcJ.SOLUTION: There is provided an R-T-B based permanent magnet in which, R is a rare earth element, T is an element other than a rare earth element, B, C, O or N, and B is boron. R at least includes Tb, and T at least includes Fe, Cu, Co and Ga. A total of R content is 28.05-30.60 mass%, Cu content is 0.04-0.50 mass%, Co content is 0.5-3.0 mass%, Ga content is 0.08-0.30 mass%, and B content is 0.85-0.95 mass%, relative to 100 mass% of a total mass of R, T and B. The R-T-B based permanent magnet shows a concentration distribution in which Tb concentration reduces from the outside to the inside of the R-T-B based permanent magnet.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an R-T-B permanent magnet.

  A rare earth permanent magnet having an R-T-B system composition is a magnet having excellent magnetic properties, and many studies have been made with the aim of further improving the magnetic properties. In general, the residual magnetic flux density (residual magnetization) Br and the coercive force HcJ are used as indices representing the magnetic characteristics. It can be said that magnets having these values have excellent magnetic properties.

  Patent Document 1 describes a rare earth permanent magnet in which a magnet body is immersed in a slurry in which fine powders containing various rare earth elements are dispersed in water or an organic solvent, and then heated and diffused at grain boundaries.

International Publication No. 2006/43348 Pamphlet

  An object of the present invention is to provide an RTB-based permanent magnet having a high residual magnetic flux density Br and a coercive force HcJ.

In order to achieve the above object, the RTB-based permanent magnet of the present invention is:
An R-T-B permanent magnet in which R is a rare earth element, T is an element other than rare earth elements, B, C, O and N, and B is boron,
R contains at least Tb,
T contains at least Fe, Cu, Co and Ga,
The total mass of R, T and B is 100% by mass,
The total content of R is 28.05 mass% to 30.60 mass%,
The Cu content is 0.04 mass% to 0.50 mass%,
Co content of 0.5 mass% to 3.0 mass%,
Ga content is 0.08 mass% to 0.30 mass%,
The content of B is 0.85% by mass to 0.95% by mass,
The concentration distribution of Tb is a concentration distribution that decreases from the outside toward the inside of the RTB-based permanent magnet.

  The RTB-based permanent magnet of the present invention can improve the residual magnetic flux density Br and the coercive force HcJ by having the above characteristics.

  R contains at least a light rare earth element, the total content of R is 29.25% by mass to 30.60% by mass, and the total content of the light rare earth element is 29.1% by mass to 30.1% by mass. Also good.

  R may contain at least Nd.

  R may contain at least Pr, and the Pr content may be greater than 0 and 10.0% by mass or less.

  R may contain at least Nd and Pr.

T may further contain Al,
The content of Al may be 0.15% by mass to 0.30% by mass.

T may further contain Zr,
The content of Zr may be 0.10% by mass to 0.30% by mass.

  Further, C may be contained, and the content of C may be 1100 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  Further, N may be included, and the content of N may be 1000 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  Furthermore, O may be contained, and the content of O may be 1000 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  Tb / C may be 0.10 to 0.95 in atomic ratio.

  When the total content of R is TRE, TRE / B may be 2.2 to 2.7 in terms of atomic ratio.

  14B / (Fe + Co) may be greater than 0 and 1.01 or less in atomic ratio.

It is a schematic diagram of the RTB system permanent magnet which concerns on this embodiment.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

<R-T-B permanent magnet>
The RTB-based permanent magnet 1 according to the present embodiment has particles and grain boundaries made of R ₂ T ₁₄ B crystals.

  The R-T-B permanent magnet 1 according to the present embodiment can have any shape.

  The R-T-B system permanent magnet 1 according to the present embodiment includes a plurality of specific elements including Tb in a specific range of content, so that residual magnetic flux density Br, coercive force HcJ, corrosion resistance, and manufacturing stability Can be improved.

  Further, the RTB system permanent magnet 1 according to the present embodiment has a concentration distribution in which the concentration of Tb decreases from the outside to the inside of the RTB system permanent magnet 1.

  Specifically, as shown in FIG. 1, when the rectangular parallelepiped R-T-B system permanent magnet 1 according to the present embodiment has a surface portion and a center portion, the Tb content in the surface portion is the center. 2% or more higher than the Tb content in the part, or 5% or more, or 10% or more. The surface portion refers to the surface of the RTB permanent magnet 1. For example, points C and C ′ in FIG. 1 (centers of gravity of the surfaces facing each other in FIG. 1) are surface portions. The center portion refers to the center of the R-T-B system permanent magnet 1. For example, it refers to a half of the thickness of the R-T-B permanent magnet 1. For example, the point M (the middle point between the point C and the point C ′) in FIG. 1 is the central portion.

  Although there is no particular limitation on the method for generating the above-described concentration distribution in the Tb content, the Tb concentration distribution can be generated in the magnet by Tb grain boundary diffusion described later.

  R represents a rare earth element. The rare earth elements include Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. Further, in the R-T-B system permanent magnet according to the present embodiment, T always contains Tb as R. R preferably contains Nd.

  Generally, rare earth elements are classified into light rare earth elements and heavy rare earth elements. Light rare earth elements in the R-T-B permanent magnet according to the present embodiment are Sc, Y, La, Ce, Pr, Nd, Sm, Eu. The heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  T represents an element other than rare earth elements, B, C, O and N. In the RTB-based permanent magnet according to the present embodiment, T includes at least Fe, Co, Cu, and Ga. Further, for example, one or more elements among elements such as Al, Mn, Zr, Ti, V, Cr, Ni, Nb, Mo, Ag, Hf, Ta, W, Si, P, Bi, and Sn are defined as T. Further, it may be included.

  B is boron.

  The total content of R in the RTB-based permanent magnet according to the present embodiment is 28.05% by mass or more and 30.60% by mass or less, where the total mass of R, T, and B is 100% by mass. When the total content of R is less than 28.05% by mass, the coercive force HcJ decreases. When the total content of R is more than 30.60% by mass, the residual magnetic flux density Br decreases. The total content of R may be 28.25% by mass to 30.60% by mass, 29.25% by mass to 30.60% by mass, or 29.45% by mass to 30.60% by mass. 29.45 mass% or more and 30.45 mass% or less.

  In the case where the total content of light rare earth elements in the RTB-based permanent magnet according to the present embodiment is TRL, and the total mass of R, T, and B is 100% by mass, TRL is 27.9% by mass. It may be 30.1% by mass or less, or 29.1% by mass or more and 30.1% by mass or less. When TRL is within the range, the residual magnetic flux density and the coercive force HcJ can be further improved.

  Furthermore, the content of Nd is arbitrary in the RTB-based permanent magnet of the present embodiment. Further, the total mass of R, T, and B is 100 mass%, and the content of Nd may be 0 mass% to 30.1 mass%, or may be 0 mass% to 29.6 mass%. 19.6% by mass to 29.6% by mass, 19.6% by mass to 24.6% by mass, and 19.6% by mass to 22.6% by mass. Moreover, content of Pr is 0.0 mass%-10.0 mass%. That is, it is not necessary to contain Pr. The RTB-based permanent magnet of this embodiment may contain at least Nd and Pr as R. The Pr content may be 5.0% by mass or more and 10.0% by mass or less. It is good also as 5.0 mass% or more and 7.5 mass% or less. Further, when the Pr content is 10.0% by mass or less, the temperature change rate of the coercive force HcJ is excellent. In particular, from the viewpoint of increasing the coercive force HcJ at a high temperature, the Pr content may be 0.0 mass% to 7.5 mass%.

  Further, the RTB-based permanent magnet of the present embodiment may include a heavy rare earth element in a total amount of 1.0% by mass or less, with the total mass of R, T, and B being 100% by mass. As the heavy rare earth element, Tb is essential and Dy may be further included. When the content of heavy rare earth elements is 1.0% by mass or less in total, the residual magnetic flux density can be easily kept good. The heavy rare earth element may be substantially only Tb. In this case, the content of Tb may be 0.15% by mass or more and 1.0% by mass or less, 0.15% by mass or more and 0.75% by mass or less, and 0.15% by mass or more and 0.5% by mass or less. . When the Tb content is less than 0.15% by mass, the coercive force HcJ tends to decrease. If the content of Tb exceeds 1.0% by mass, the residual magnetic flux density Br tends to decrease.

  The Cu content is 0.04 mass% or more and 0.50 mass% or less, where the total mass of R, T, and B is 100 mass%. If the Cu content is less than 0.04% by mass, the coercive force HcJ tends to decrease. When the Cu content exceeds 0.50 mass%, the coercive force HcJ tends to decrease, and the residual magnetic flux density Br tends to decrease. Moreover, 0.10 mass% or more and 0.50 mass% or less may be sufficient as content of Cu, and 0.10 mass% or more and 0.30 mass% or less may be sufficient. Corrosion resistance tends to be improved by containing 0.10% by mass or more of Cu.

  The Ga content is 0.08 mass% or more and 0.30 mass% or less, where the total mass of R, T, and B is 100 mass%. By containing 0.08% by mass or more of Ga, the coercive force HcJ is sufficiently improved. If it exceeds 0.30% by mass, a secondary phase (for example, an R—T—Ga phase) is easily generated, and the residual magnetic flux density Br decreases. Moreover, 0.10 mass% or more and 0.25 mass% or less may be sufficient as content of Ga.

  The Co content is 0.5% by mass or more and 3.0% by mass or less, where the total mass of R, T, and B is 100% by mass. Corrosion resistance is improved by containing Co. When the Co content is less than 0.5% by mass, the corrosion resistance of the RTB-based permanent magnet is deteriorated. If the Co content exceeds 3.0% by mass, the effect of improving the corrosion resistance reaches its peak and the cost is increased. Moreover, 1.0 mass% or more and 3.0 mass% or less may be sufficient as content of Co.

  The content of Al may be not less than 0.15% by mass and not more than 0.30% by mass, where the total mass of R, T and B is 100% by mass. The coercive force HcJ can be improved by setting the Al content to 0.15% by mass or more. Furthermore, the change in magnetic properties (particularly the coercive force HcJ) with respect to changes in the aging temperature or the heat treatment temperature after grain boundary diffusion is reduced, and the variation in properties during mass production is reduced. That is, manufacturing stability is improved. When the Al content is 0.30% by mass or less, the residual magnetic flux density Br can be improved. Furthermore, the temperature change rate of the coercive force HcJ can be improved. Moreover, 0.15 mass% or more and 0.25 mass% or less may be sufficient as content of Al. When the Al content is 0.15 mass% or more and 0.25 mass% or less, the change in magnetic properties (particularly the coercive force HcJ) with respect to the change in aging temperature or heat treatment temperature after grain boundary diffusion is further reduced.

  The content of Zr may be not less than 0.10% by mass and not more than 0.30% by mass, where the total mass of R, T and B is 100% by mass. By containing Zr, abnormal grain growth during sintering is suppressed, and the squareness ratio Hk / HcJ and the magnetization rate under a low magnetic field are improved. By setting the Zr content to 0.10% by mass or more, the effect of suppressing abnormal grain growth during sintering due to the Zr content increases, and the squareness ratio Hk / HcJ and the magnetization rate under a low magnetic field are improved. . By setting it to 0.30 mass% or less, the residual magnetic flux density Br can be improved. Moreover, 0.15 mass% or more and 0.30 mass% or less may be sufficient as content of Zr, and 0.15 mass% or more and 0.25 mass% or less may be sufficient. By setting the Zr content to 0.15% by mass or more, the sintering stable temperature range is widened. That is, the effect of suppressing abnormal grain growth is further increased during sintering. And the dispersion | variation in a characteristic becomes small and manufacturing stability improves.

  Further, the RTB-based permanent magnet according to this embodiment may include Mn. When Mn is contained, the content of Mn may be 0.02% by mass to 0.10% by mass, where the total mass of R, T, and B is 100% by mass. When the Mn content is 0.02% by mass or more, the residual magnetic flux density Br tends to be improved and the coercive force HcJ tends to be improved. When the Mn content is 0.10% by mass or less, the coercive force HcJ tends to be improved. Moreover, 0.02 mass% or more and 0.06 mass% or less may be sufficient as content of Mn.

  The content of B in the RTB-based permanent magnet according to the present embodiment is 0.85% by mass or more and 0.95% by mass or less, where the total mass of R, T, and B is 100% by mass. When B is less than 0.85% by mass, it is difficult to achieve high squareness. That is, it becomes difficult to improve the squareness ratio Hk / HcJ. When B is more than 0.95% by mass, the squareness ratio Hk / HcJ decreases. Moreover, 0.88 mass% or more and 0.94 mass% or less may be sufficient as content of B. By setting the B content to 0.88 mass% or more, the residual magnetic flux density Br tends to be further improved. By setting the B content to 0.94 mass% or less, the coercive force HcJ tends to be further improved.

  Further, when TRE is the total content of R elements, TRE / B may be 2.2 or more and 2.7 or less in atomic ratio. Moreover, even if it is 2.24 or more and 2.65 or less, 2.31 or more and 2.65 or less, 2.36 or more and 2.61 or less, 2.36 or more and 2.56 or less, 2.37 or more and 2.56 or less Good. When TRE / B is within the above range, the residual magnetic flux density and the coercive force HcJ are improved.

  Further, 14B / (Fe + Co) may be greater than 0 and 1.01 or less in terms of the atomic ratio. When 14B / (Fe + Co) is 1.01 or less, the squareness ratio tends to be improved. 14B / (Fe + Co) may be 1.00 or less.

  Further, the atomic ratio Tb / C obtained by dividing the Tb content by the C content may be 0.10 or more and 0.95 or less. When Tb / C is within the above range, the temperature characteristic of the coercive force HcJ is improved. Furthermore, the coercive force HcJ at high temperature is also improved. Tb / C may be 0.10 or more and 0.65 or less, 0.15 or more and 0.50 or less, or 0.20 or more and 0.45 or less. Moreover, 0.13 or more and 0.63 or less, 0.17 or more and 0.63 or less, 0.21 or more and 0.63 or less, and 0.21 or more and 0.44 or less may be sufficient. Furthermore, when Tb / C is within the above range when TRL is 29.1 mass% or more and 30.1 mass% or less, the temperature characteristics of coercive force HcJ and the coercive force HcJ at high temperature are further improved.

  The content of carbon (C) in the RTB-based permanent magnet according to the present embodiment may be 1100 ppm or less, 1000 ppm or less, or 900 ppm with respect to the total mass of the RTB-based permanent magnet. It may be the following. Further, it may be 600 ppm to 1100 ppm, 600 ppm to 1000 ppm, or 600 ppm to 900 ppm. The coercive force HcJ tends to be improved by setting the carbon content to 1100 ppm or less. In particular, from the viewpoint of improving the coercive force HcJ, the carbon content can be 900 ppm or less. In addition, producing an R-T-B permanent magnet having a carbon content of less than 600 ppm has a heavy load on the process and causes an increase in cost.

  In particular, from the viewpoint of improving the squareness ratio, the carbon content can be set to 800 ppm to 1100 ppm.

  In the RTB-based permanent magnet according to this embodiment, the content of nitrogen (N) may be 1000 ppm or less, 700 ppm or less, or 600 ppm or less with respect to the total mass of the RTB-based permanent magnet. It is good. Moreover, 250 ppm-1000 ppm, 250 ppm-700 ppm, or 250 ppm-600 ppm may be sufficient. The smaller the nitrogen content, the easier the coercive force HcJ improves. In addition, producing an R—T—B system permanent magnet having a nitrogen content of less than 250 ppm places a large load on the process, which increases costs.

    In the RTB-based permanent magnet according to the present embodiment, the content of oxygen (O) may be 1000 ppm or less and 800 ppm or less with respect to the total mass of the RTB-based permanent magnet. It may be 700 ppm or less, or 500 ppm or less. Moreover, 350 ppm-500 ppm may be sufficient. However, although there is no particular lower limit of the oxygen content, producing an R—T—B system permanent magnet having a content of less than 350 ppm places a heavy load on the process and causes an increase in cost.

  Furthermore, while reducing the total content of R before grain boundary diffusion described below to 29.1% by mass or more, the oxygen content is reduced to 1000 ppm or less, 800 ppm or less, 700 ppm or less, or 500 ppm or less during sintering. Deformation can be suppressed and manufacturing stability can be improved. In addition, when the total content of R before grain boundary diffusion described later is 29.1% by mass or more, the total content of R after grain boundary diffusion is, for example, 29.25% by mass or more.

  The reason why the deformation during sintering can be suppressed by reducing the oxygen content while keeping the total content of R at or above a predetermined amount is considered to be as follows. The sintering mechanism of the R-T-B system permanent magnet is liquid phase sintering, and a grain boundary phase component called an R-rich phase generates a liquid phase during sintering and promotes densification. On the other hand, O easily reacts with the R-rich phase, and when the amount of O increases, a rare earth oxide phase is formed and the amount of R-rich phase decreases. Generally, a very small amount of oxidizing impurity gas exists in the sintering furnace. For this reason, in the sintering process, the R-rich phase may be oxidized in the vicinity of the surface of the molded body, and the amount of R-rich phase may locally decrease. A composition with a large total content of R and a small amount of O has a large amount of R-rich phase, and the effect of oxidation on the shrinkage behavior during sintering is small. In a composition having a small total R content and / or a large amount of O, the amount of R-rich phase is small, so that oxidation during the sintering process affects the shrinkage behavior during sintering. As a result, deformation of the sintered body occurs due to partial shrinkage, that is, changes in dimensions. Therefore, deformation during sintering can be suppressed by reducing the oxygen content while keeping the total content of R at or above a predetermined amount.

  In addition, the method generally known conventionally can be used for the measuring method of the various components contained in the RTB system permanent magnet which concerns on this embodiment. The amount of various elements is measured by, for example, fluorescent X-ray analysis and inductively coupled plasma emission spectroscopy (ICP analysis). The oxygen content is measured, for example, by an inert gas melting-non-dispersive infrared absorption method. The carbon content is measured by, for example, combustion in an oxygen stream-infrared absorption method. The nitrogen content is measured, for example, by an inert gas melting-thermal conductivity method.

  Further, the RTB-based permanent magnet according to the present embodiment includes a plurality of main phase particles and grain boundaries. The main phase particles may be core-shell particles including a core and a shell covering the core. And at least the shell may contain a heavy rare earth element or Tb.

  By allowing the heavy rare earth element to exist in the shell portion, the magnetic properties of the RTB-based permanent magnet can be improved efficiently.

  In the present embodiment, the ratio of the heavy rare earth element to the light rare earth element (heavy rare earth element / light rare earth element (molar ratio)) is at least twice the ratio in the main phase particle center (core). Is defined as a shell.

  The thickness of the shell is not particularly limited, but may be 500 nm or less. The particle size of the main phase particles is not particularly limited, but may be 3.0 μm or more and 6.5 μm or less.

  The method of using the main-phase particles as the core-shell particles is arbitrary. For example, there is a method by grain boundary diffusion described later. The heavy rare earth element diffuses in the grain boundary, and the heavy rare earth element replaces the rare earth element R on the surface of the main phase particle, thereby forming a shell having a high ratio of the heavy rare earth element, and the core-shell particle is obtained.

  Hereinafter, although the manufacturing method of a RTB system permanent magnet is explained in detail, the manufacturing method of an RTB system permanent magnet is not restricted to this, and other publicly known methods may be used.

[Preparation process of raw material powder]
The raw material powder can be produced by a known method. In the present embodiment, the case of the one alloy method using a single alloy will be described, but a so-called two alloy method in which a raw material powder is prepared by mixing first and second alloys having different compositions may be used.

  First, a raw material alloy of an R-T-B system permanent magnet is prepared (alloy preparation step). In the alloy preparation process, a raw material alloy having a desired composition is prepared by melting a raw material metal corresponding to the composition of the R-T-B system permanent magnet according to the present embodiment by a known method and then casting the raw material metal.

  As a raw material metal, for example, a rare earth metal or a rare earth alloy, pure iron, ferroboron, a metal such as Co or Cu, or an alloy or compound thereof can be used. The casting method for casting the raw material alloy from the raw metal may be any method. In order to obtain an R-T-B permanent magnet having high magnetic properties, a strip casting method may be used. The obtained raw material alloy may be homogenized by a known method as necessary. At this time, the heavy rare earth element added to the raw material metal may be Dy alone, or the heavy rare earth element may not be added. In particular, at this time, Tb may be added only by grain boundary diffusion described later without adding Tb, and the raw material cost can be suppressed.

  After producing the raw material alloy, it is pulverized (pulverization step). In addition, the atmosphere of each process from a grinding | pulverization process to a sintering process can be made into a low oxygen concentration from a viewpoint of obtaining a high magnetic characteristic. For example, the oxygen concentration in each step may be 200 ppm or less. By controlling the oxygen concentration in each step, the amount of oxygen contained in the RTB-based permanent magnet can be controlled.

  Hereinafter, the pulverization step is performed in two stages: a coarse pulverization step of pulverizing until the particle size is about several hundred μm to several mm, and a fine pulverization step of pulverizing until the particle size is about several μm. As will be described below, it may be carried out in one stage only with the fine grinding process.

  In the coarse pulverization step, coarse pulverization is performed until the particle size becomes approximately several hundred μm to several mm. Thereby, coarsely pulverized powder is obtained. The method of coarse pulverization may be performed by any method, and can be performed by a known method such as a method of performing hydrogen occlusion and a method of using a coarse pulverizer. When performing hydrogen occlusion and pulverization, the amount of nitrogen contained in the RTB-based permanent magnet can be controlled by controlling the nitrogen gas concentration in the atmosphere during the dehydrogenation treatment.

  Next, the obtained coarsely pulverized powder is finely pulverized until the average particle diameter becomes about several μm (a fine pulverization step). Thereby, finely pulverized powder (raw material powder) is obtained. The average particle size of the finely pulverized powder may be 1 μm to 10 μm, 2 μm to 6 μm, or 3 μm to 5 μm. By controlling the nitrogen gas concentration in the atmosphere of the fine pulverization step, the amount of nitrogen contained in the RTB-based permanent magnet can be controlled.

  The pulverization is performed by an arbitrary method. For example, it is carried out by a method using various pulverizers.

  When the coarsely pulverized powder is finely pulverized, by adding various pulverization aids such as lauric acid amide and oleic acid amide, a finely pulverized powder with high orientation can be obtained during molding. Further, the amount of carbon contained in the RTB-based permanent magnet can be controlled by changing the amount of the grinding aid added.

[Molding process]
In the forming step, the finely pulverized powder is formed into a desired shape. Molding may be performed by any method. In this embodiment, the finely pulverized powder is filled in a mold and pressed in a magnetic field. Since the main phase crystal is oriented in a specific direction in the obtained compact, an RTB permanent magnet having a higher residual magnetic flux density Br is obtained.

  The pressurization at the time of molding can be performed at 20 MPa to 300 MPa. The applied magnetic field can be 950 kA / m or more, and can be 950 kA / m to 1600 kA / m. The magnetic field to be applied is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  In addition, as a shaping | molding method, the wet shaping | molding which shape | molds the slurry which disperse | distributed finely pulverized powder in solvent, such as oil other than the dry type | molding which shape | molds finely pulverized powder as it is as mentioned above can also be applied.

The shape of the molded body obtained by molding the finely pulverized powder can be any shape. The density of the molded body at this point can be ^{4.0Mg / m 3 ~4.3Mg / m 3} .

[Sintering process]
A sintering process is a process of sintering a molded object in a vacuum or inert gas atmosphere, and obtaining a sintered compact. The sintering temperature needs to be adjusted depending on various conditions such as composition, pulverization method, difference in particle size and particle size distribution, etc., but for the molded body, for example, 1000 ° C. or higher and 1200 ° C. in vacuum or in the presence of an inert gas. Baking is performed by performing a heating process at a temperature of 1 ° C. or less and 1 hour or more and 20 hours or less. Thereby, a high-density sintered compact is obtained. In the present embodiment, a sintered body having a density of at least 7.45 Mg / m ³ or more is obtained. The density of the sintered body may be 7.50 Mg / m ³ or more.

[Aging process]
The aging treatment step is a step of heat-treating the sintered body at a temperature lower than the sintering temperature. There is no particular limitation on whether or not to perform the aging treatment, and the number of aging treatments is not particularly limited, and is appropriately performed according to desired magnetic characteristics. Moreover, when employ | adopting the grain-boundary diffusion process mentioned later, a grain-boundary diffusion process may serve as the aging treatment process. In the R-T-B system permanent magnet according to the present embodiment, aging treatment is performed twice. Hereinafter, an embodiment in which the aging process is performed twice will be described.

  The first aging process is the first aging process, the second aging process is the second aging process, the aging temperature of the first aging process is T1, and the aging temperature of the second aging process is T2.

  There is no restriction | limiting in particular in temperature T1 and aging time in a 1st temporary effect process. It can be 1 hour-10 hours at 700 degreeC or more and 900 degrees C or less.

  There is no restriction | limiting in particular in temperature T2 and aging time in a 2nd aging process. It can be 1 hour-10 hours at 500 degreeC or more and 700 degrees C or less.

  By such an aging treatment, it is possible to improve the magnetic properties of the RTB permanent magnet finally obtained, particularly the coercive force HcJ.

  Hereinafter, a method for diffusing Tb at the grain boundary in the R-T-B permanent magnet according to the present embodiment will be described.

[Processing process (before grain boundary diffusion)]
You may have the process of processing the RTB type | system | group permanent magnet which concerns on this embodiment in a desired shape before a grain boundary diffusion as needed. Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.

  [Grain boundary diffusion process]

Grain boundary diffusion is performed by attaching a heavy rare earth metal, a compound or alloy containing heavy rare earth element (Tb in the present embodiment), etc. to the surface of an R-T-B permanent magnet by coating or vapor deposition. It can be implemented by performing. The coercive force HcJ of the RTB-based permanent magnet finally obtained can be further improved by the grain boundary diffusion of the heavy rare earth element. Tb is preferred as the heavy rare earth element to be diffused at the grain boundaries in the sintered body. By using Tb, a higher coercive force HcJ can be obtained.

  In the embodiment described below, a paint containing Tb is prepared, and the paint is applied to the surface of the RTB-based permanent magnet.

  The aspect of the paint is arbitrary. What is used as a compound containing Tb and what is used as a solvent or a dispersion medium are also arbitrary. Moreover, the density | concentration of Tb in a coating material is arbitrary.

  The diffusion treatment temperature in the grain boundary diffusion step according to this embodiment can be set to 800 ° C. to 950 ° C. The diffusion treatment time can be 1 hour to 50 hours. Note that the grain boundary diffusion step may also serve as the aging treatment step described above.

  By setting the above diffusion treatment temperature and diffusion treatment time, it is easy to keep the manufacturing cost low and to make the Tb concentration distribution suitable.

  Further, after the grain boundary diffusion treatment, heat treatment may be further performed. In this case, the heat treatment temperature can be 450 ° C. to 600 ° C. The heat treatment time can be 1 hour to 10 hours. Such heat treatment can improve the magnetic properties of the finally obtained RTB-based permanent magnet, particularly the coercive force HcJ.

  In addition, the production stability of the RTB-based permanent magnet according to the present embodiment can be confirmed by the magnitude of the change in magnetic characteristics with respect to the change in aging temperature, diffusion treatment temperature, or heat treatment temperature after diffusion treatment. Hereinafter, although the diffusion treatment process will be described, the same applies to the aging process and the heat treatment after the diffusion treatment.

  For example, if the amount of change in the magnetic characteristics with respect to the change in the diffusion treatment temperature is large, the magnetic characteristics change with a slight change in the diffusion treatment temperature. For this reason, the range of the diffusion treatment temperature allowed in the grain boundary diffusion step is narrowed, and the production stability is lowered. On the other hand, if the amount of change in the magnetic characteristics with respect to the change in the diffusion treatment temperature is small, the magnetic characteristics will hardly change even if the diffusion treatment temperature changes. For this reason, the range of the diffusion treatment temperature allowed in the grain boundary diffusion step is widened, and the production stability is increased. Furthermore, since the grain boundary can be diffused at a high temperature for a short time, the manufacturing cost can be reduced.

[Processing process (after grain boundary diffusion)]
After the grain boundary diffusion step, various types of processing of the RTB-based permanent magnet may be performed. There is no restriction | limiting in particular in the kind of processing to implement. For example, shape processing such as cutting and grinding, and surface processing such as chamfering processing such as barrel polishing may be performed.

  The RTB system permanent magnet according to the present embodiment obtained by the above method becomes an RTB system permanent magnet product by being magnetized.

  The RTB system permanent magnet according to the present embodiment obtained in this way has desired characteristics. Specifically, the residual magnetic flux density Br and the coercive force HcJ are high, and the corrosion resistance and manufacturing stability are also excellent.

  The R-T-B system permanent magnet according to the present embodiment is suitably used for applications such as motors and generators.

  Note that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

The manufacturing method of the RTB-based permanent magnet is not limited to the above method, and may be changed as appropriate. For example, although the manufacturing method of said R-T-B system permanent magnet is a manufacturing method by sintering, the R-T-B system permanent magnet which concerns on this embodiment may be manufactured by hot processing. The method for producing an RTB-based permanent magnet by hot working includes the following steps.
(A) Melting and quenching step of dissolving raw metal and quenching the obtained bath water to obtain a ribbon (b) Grinding step of pulverizing the ribbon to obtain a flaky raw powder (c) Crushed raw material powder (D) Preheating step for preheating the cold formed body (e) Hot forming step for hot forming the preheated cold formed body (f) Hot forming body A hot plastic working process in which plastic deformation is performed into a predetermined shape.
(G) Aging treatment step of aging treatment of an R-T-B system permanent magnet The steps after the aging treatment step are the same as in the case of manufacturing by sintering.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

(Experimental example 1)
(Production of RTB-based sintered magnet)
As raw materials, Nd, Pr, electrolytic iron, and a low carbon ferroboron alloy were prepared. Furthermore, Al, Ga, Cu, Co, Mn, and Zr were prepared in the form of a pure metal or an alloy with Fe.

  Using the raw material, a raw material alloy was prepared by a strip casting method so that the magnet composition finally obtained through grain boundary diffusion described later has the composition of each sample shown in Tables 1 and 2. The contents (ppm) of C, N, and O shown in Tables 1 and 2 represent contents relative to the total mass of the magnet. Although Fe is not shown in Table 2, the contents (mass%) of elements other than C, N, and O shown in Tables 1 and 2 are Nd, Pr, Tb, B, Al, Ga, Cu , Co, Mn, Zr and Fe, the total content being 100% by mass. The alloy thickness of the raw material alloy was 0.2 mm to 0.4 mm.

  Next, hydrogen was occluded by flowing hydrogen gas to the raw material alloy at room temperature for 1 hour. Next, the atmosphere was switched to Ar gas, dehydrogenation treatment was performed at 600 ° C. for 1 hour, and the raw material alloy was occluded by hydrogen. For sample numbers 81 to 83, the nitrogen gas concentration in the atmosphere during the dehydrogenation treatment was adjusted so that the nitrogen content was a predetermined amount. Furthermore, after cooling, a sieve having a particle size of 425 μm or less was obtained using a sieve. In addition, from the hydrogen occlusion pulverization to the sintering step described later, a low oxygen atmosphere with an oxygen concentration of less than 200 ppm was always used. For sample numbers 74 to 78, the oxygen concentration was adjusted so that the oxygen content was a predetermined amount.

  Subsequently, 0.1% oleic amide by mass ratio was added as a grinding aid to the raw alloy powder after using hydrogen storage and sieving, and mixed. For sample numbers 63 to 68, the addition amount of the grinding aid was adjusted so that the carbon content was a predetermined amount.

  Subsequently, it was finely pulverized in a nitrogen stream using a collision plate type jet mill device to obtain a fine powder having an average particle size of 3.9 μm to 4.2 μm. Sample numbers 79 and 80 were finely pulverized in a mixed gas stream of Ar and nitrogen, and the nitrogen gas concentration was adjusted so that the nitrogen content was a predetermined amount. The average particle diameter is an average particle diameter D50 measured with a laser diffraction particle size distribution meter.

The obtained fine powder was molded in a magnetic field to produce a molded body. The applied magnetic field at this time is a static magnetic field of 1200 kA / m. The pressing force during molding was 98 MPa. The magnetic field application direction and the pressurizing direction were orthogonal to each other. When the density of the molded body at this time was measured, the density of all the molded bodies was within the range of 4.10 Mg / m ^{3 to} 4.25 Mg / m ³ .

Next, the molded body was sintered to obtain a sintered body. The optimum sintering conditions differed depending on the composition and the like, but were held for 4 hours within the range of 1040 ° C to 1100 ° C. The sintering atmosphere was in a vacuum. At this time, the sintered density was in the range of 7.45 Mg / m ^{3 to} 7.55 Mg / m ³ . Thereafter, in the Ar atmosphere and atmospheric pressure, the first temporary effect treatment was performed for 1 hour at the first temporary effect temperature T1 = 850 ° C., and further the second aging treatment was performed for 1 hour at the second aging temperature T2 = 520 ° C. .

  Thereafter, the sintered body after the aging treatment was processed into 14 mm × 10 mm × 4.2 mm (thickness in the direction of easy magnetization axis: 4.2 mm) by a vertical to prepare a sintered body before Tb grain boundary diffusion described later.

Further, the sintered body obtained in the above-described process is immersed in a mixed solution of nitric acid and ethanol containing 3% by mass of nitric acid with respect to 100% by mass of ethanol for 3 minutes and then immersed in ethanol for 1 minute. It was. The etching process of immersing in the mixed solution for 3 minutes and then immersing in ethanol for 1 minute was performed twice. Next, a slurry obtained by dispersing TbH ₂ particle average particle diameter D50 = 10.0 μm in ethanol over the entire surface of the sintered body after the etching treatment is 0.2% by mass to 1% by mass ratio of Tb to mass of the magnet. 2% by mass was applied. The coating amount was changed so that the Tb contents shown in Tables 1 and 2 were obtained.

  The slurry was applied and dried, followed by diffusion treatment at 930 ° C. for 18 hours while flowing Ar at atmospheric pressure, followed by heat treatment at 520 ° C. for 4 hours. Next, the surface of a 14 × 10 × 4.2 mm sample was scraped off by 0.1 mm for each surface, and R-T-B system sintered magnets of the samples shown in Tables 1 and 2 were obtained.

  The average composition of each R-T-B system sintered magnet obtained was measured. Each sample was pulverized by a stamp mill and subjected to analysis. Various element amounts were measured by fluorescent X-ray analysis. The content of boron (B) was measured by ICP analysis. The oxygen content was measured by an inert gas melting-non-dispersive infrared absorption method, the carbon content was measured by combustion in an oxygen stream-infrared absorption method, and the nitrogen content was measured by an inert gas melting-thermal conductivity method. . The results are shown in Tables 1 and 2. In the present example, the total TRE of the R content is 28.20% by mass or more and 30.50% by mass or less.

  About each obtained R-T-B system sintered magnet, the magnetic characteristic was evaluated with the BH tracer. Magnetic properties were evaluated after magnetizing with a 4000 kA / m pulsed magnetic field. Since the sintered magnet was thin, three of the sintered magnets were stacked and evaluated. The results are shown in Tables 1 and 2.

In general, the residual magnetic flux density and the coercive force HcJ are in a trade-off relationship. That is, the higher the residual magnetic flux density, the lower the coercive force HcJ, and the higher the coercive force HcJ, the lower the residual magnetic flux density. Therefore, in this embodiment, a performance index PI (Potential Index) for comprehensively evaluating the residual magnetic flux density and the coercive force HcJ is set. When the magnitude of the residual magnetic flux density measured in mT units is Br (mT) and the coercive force magnitude measured in kA / m units is HcJ (kA / m),
PI = Br + 25 × HcJ × 4π / 2000
It was. In this example, when PI ≧ 1745, the residual magnetic flux density and the coercive force HcJ are considered good. In the case of PI ≧ 1765, the residual magnetic flux density and the coercive force HcJ were further improved. Further, the squareness ratio Hk / HcJ was determined to be good when it was 90% or more. In Tables 1 and 2, samples with good PI and squareness ratios were marked with ◯, and samples with poor ratios were marked with ×. In this embodiment, the squareness ratio Hk / HcJ is the magnetic field when the magnetization is 90% of Br in the second quadrant (JH demagnetization curve) of the magnetization J-magnetic field H curve. m) is calculated as Hk / HcJ × 100 (%).

Moreover, the corrosion resistance test was done with respect to each R-T-B system sintered magnet. The corrosion resistance test was carried out by a PCT test (pressure cooker test) under saturated vapor pressure. Specifically, the R-T-B system sintered magnet was placed in an environment of 2 atm and 100% RH for 1000 hours, and the mass change before and after the test was measured. It was judged that the corrosion resistance was good when the mass reduction per surface area of the magnet was 3 mg / cm ² or less. All of the samples subjected to the corrosion resistance test this time had good corrosion resistance.

  In Table 1, TRE and B were varied. Further, Nd and Pr were contained so that the mass ratio of Nd and Pr was approximately 3: 1. In Table 2, the content of each component other than B was changed. In Sample Nos. 84 to 87, TRE was fixed and the contents of Nd and Pr were changed.

  From Table 1 and Table 2, all Examples had good PI and squareness ratios. On the other hand, in all the comparative examples, one or more of PI and squareness ratio were not good. In addition, about the RTB type sintered magnets of all Examples and Comparative Examples, the Tb concentration distribution was analyzed using an electron probe microanalyzer (EPMA), and the Tb concentration distribution was directed from the outside to the inside. It was confirmed that the concentration distribution decreased.

1 ... R-T-B permanent magnet

Claims (7)

An R-T-B permanent magnet in which R is a rare earth element, T is an element other than rare earth elements, B, C, O and N, and B is boron,
R contains at least Tb,
T contains at least Fe, Cu, Co and Ga,
The total mass of R, T and B is 100% by mass,
The total content of R is 28.05 mass% to 30.60 mass%,
The Cu content is 0.04 mass% to 0.50 mass%,
Co content of 0.5 mass% to 3.0 mass%,
Ga content is 0.08 mass% to 0.30 mass%,
The content of B is 0.85% by mass to 0.95% by mass,
An RTB-based permanent magnet, wherein the concentration distribution of Tb is a concentration distribution that decreases from the outside to the inside of the RTB-based permanent magnet.   At least a light rare earth element is contained as R, the total content of R is 29.25% by mass to 30.60% by mass, and the total content of the light rare earth element is 29.1% by mass to 30.1% by mass. Item 8. An R-T-B permanent magnet according to Item 1.   The RTB-based permanent magnet according to claim 1 or 2, which contains at least Nd as R.   The RTB-based permanent magnet according to any one of claims 1 to 3, wherein at least Pr is contained as R, and the content of Pr is greater than 0 and 10.0% by mass or less.   Tb / C is 0.10-0.95 by atomic ratio, The RTB system permanent magnet in any one of Claims 1-4.   The R-T-B type permanent magnet according to any one of claims 1 to 5, wherein TRE / B is 2.2 to 2.7 in terms of atomic ratio when the total content of R is TRE.   The RTB-based permanent magnet according to claim 1, wherein 14B / (Fe + Co) is greater than 0 and 1.01 or less in atomic ratio.

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